A printer for outputting a receipt or the like is widely used for various purposes such as a cashier terminal of a shop or an ATM (Automated Teller Machine) or a cash dispenser of a bank. For example, a printer outputs a receipt by printing characters or the like on a recording paper (e.g., heat sensitive paper) with a thermal head while conveying the recording paper, and cutting the recording paper upon reaching the predetermined length.
The printer includes, for example, a printer body and a cover rotatably supported by the printer body. By opening the cover, a roll of recording paper can be placed into the printer body. A thermal head may be placed in the printer body, and a platen roller may be placed in the cover. By closing the cover, the recording paper can be sandwiched between the thermal head and the platen roller. In this state where the recording paper is sandwiched between the thermal head and the platen roller, printing by the thermal head is performed. A small-sized easy-to-carry mobile printer is an example of the printer using the thermal head or the like.
[Patent Document 1]: Japanese Laid-Open Patent Publication No.: 10-250130
[Patent Document 2]: Japanese Laid-Open Patent Publication No. 2004-210444
[Patent Document 3]: Japanese Laid-Open Patent Publication No. 2008-30253
With a printer using a thermal head or the like, the printer takes a printable state by closing the lid. Whether the printer is in the printable state or not may be determined by determining whether the platen roller is in a predetermined position while the lid is closed.
More specifically, a printer 100 illustrated in FIG. 1 includes a thermal head 10. Further, the printer 100 has a platen guide 30 and a platen guide 40 provided on each of its ends for mounting a platen roller 20 thereon. The platen roller 20 is mounted to the printer by rotatably fixing the ends of the platen roller 20 to the platen guides 30, 40. The printer 100 also includes a motor 51 for conveying a recording paper by rotating the platen roller 20 and a gear box 52 for transmitting the rotation of the motor 51 to the platen roller 20.
Further, a platen lock lever 31 for retaining the platen roller 20 is rotatably joined to the platen guide 30. The platen guide 30 also includes a detection switch 32 for detecting whether the platen roller 20 is mounted in a predetermined position according to the position of the platen lock lever 31.
Similarly, a platen lock lever 41 for retaining the platen roller 20 is rotatably joined to the platen guide 40. The platen guide 40 also includes a detection switch 42 for detecting whether the platen roller 20 is mounted in a predetermined position according to the position of the platen lock lever 41.
In the example of FIG. 1, a position detection switch may be used for each of the first and second detection switches 32, 42. The position detection switch is a mechanical switch that is switched on when pressure is exerted thereto and switched off when pressure is no longer exerted thereto. That is, a normal open type detection switch may be used for each of the first and second detection switches 32, 42. More specifically, the platen roller 20 is retained at a predetermined position by the platen lock levers 31, 41 when a cover (not illustrated) is closed. When the cover is closed, the platen lock lever 31, 41 are moved to press the first and second detection switches 32, 42. Thereby, the first and second detection switches 32, 42 are switched on. Further, when the platen roller 20 is disengaged from the platen guides 30, 40 by opening the cover, the platen lock levers 31, 41 return to their initial positions. Because the platen lock levers 31, 41 no longer exert pressure to the first and second detection switches 32, 42, the first and second detection switches 32, 42 are released from the pressure and switched off.
In a case of detecting whether the platen roller 20 is mounted in a predetermined position by using the first and second detection switches 32, 42, a circuit having the first and second detection switches 32, 42 connected in series is used (see FIG. 2). More specifically, one end of the second detection switch 42 is grounded, the other end of the second detection switch 42 is connected to one end of the first detection switch 32, and the other end of the first detection switch 32 is connected to a resistor 60. Accordingly, potential is applied from a power supply Vcc to the first and second detection switches 32, 42 via the resistor 60. The detection of the platen roller 20 is performed by a potential detector 71 that detects the potential between the other terminal of the first detection switch 32 and the resistor 60.
In a case where the platen roller 20 is mounted in a predetermined position by the closing of the cover (not illustrated), the first and second detection switches 32, 42 are both switched on. Therefore, the potential detected by the potential detector 71 is low (0 V) as illustrated in FIG. 3. In a case where the platen roller 20 is disengaged from the predetermined position by the opening of the cover (not illustrated), the first and second detection switches 32, 42 are both switched off. Therefore, the potential detected by the potential detector 71 is high (Vcc) as illustrated in FIG. 3.
In a case where one of the first and second detection switches 32, 42 is switched on and the other is switched off, the potential detected by the potential detector 71 is high. This case may apply to, for example, a situation where one end of the platen roller 20 is properly mounted to the predetermined position whereas the other end of the platen roller 20 is not properly mounted to the predetermined position, or a situation where there is a malfunction due to a disconnection of one of the first and second detection switches 32, 42. In any of these situations, with the circuit illustrated in FIG. 2, the potential detector 71 detects the platen roller 20 not being mounted in the predetermined position. Therefore, with the circuit illustrated in FIG. 2, the potential detector 71 is unable to determine whether the platen roller 20 is not mounted in the predetermined position or whether there is a malfunction due to a disconnection of one of the first and second detection switches 32, 42.
Further, with the detection method using the circuit of FIG. 2, electric current constantly flows to the first and second detection switches 32, 42 when the platen roller 20 is mounted in the predetermined position in a state where the printer 100 is used. Thus, the first and second detection switches 32, 42 may malfunction due to aged deterioration caused by the constantly flowing current. Further, power consumption becomes large due to the constantly flowing current when the printer 100 is being used. Thus, in a case where the printer 100 is driven by a battery, the timespan for using the printer 100 becomes short.